An important aspect of a profilometer system is that the system be insensitive to thermally-induced drift errors. Another important aspect, for many applications, is that the profilometer system be relatively compact and consume a small amount of electrical power.
One known type of system has a single laser diode source whose output is focussed onto a sample using piezoelectrically driven focussing element(s). The scattered or reflected light is imaged by the focussing element(s) onto a quad cell focus detector, and the sample surface profile is acquired by monitoring the position of the focussing element(s).
One drawback to this "laser stylus" is a limited range/resolution ratio of 1000/1 for any resolution setting. For example, a one micron range provides one nanometer of resolution.
It is thus one object of this invention to provide a low power, compact laser probe that is substantially immune to thermally-induced errors.
It is another object of this invention to provide a low power, compact laser probe having a large dynamic range/resolution of at least (10.sup.5 :1).
It is another object of this invention to provide a low power, compact laser probe suitable for use in, by example, remote ranging and robotics control applications, in-situ metrology applications, as a replacement for conventional contact-type probes, or for use as an alignment device in semiconductor processing applications, such as in mask alignment and/or wafer positioning.
It is a further object of the invention to provide a low power, compact laser probe suitable for use as a high resolution non-contact profiler for semiconductor and other applications.